Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.87   10.541%   $93.8161   $93.82   $93.80   $93.80  
  Purchase #2 $96.55   10.230%   $106.4271   $106.43   $106.45   $106.40  
  Purchase #3 $35.82   8.226%   $38.7666   $38.77   $38.75   $38.80  
  Purchase #4 $106.85   6.381%   $113.6681   $113.67   $113.65   $113.70  
  Purchase #5 $110.68   10.792%   $122.6246   $122.62   $122.60   $122.60  
  Purchase #6 $163.71   10.859%   $181.4873   $181.49   $181.50   $181.50  
  Purchase #7 $98.64   10.748%   $109.2418   $109.24   $109.25   $109.20  
  7 purchase totals = $697.12       $766.0316   $766.04   $766.00   $766.00